Various types of systems have been employed as signal sources for displays used in different types of audio-visual display settings. For example, movies are typically presented using a film projector by advancing a strip of film through the projector, illuminating a portion of the film and conditioning light transmitted through the film for projection on a screen. In some other types of systems, a pre-recorded video tape recorder or player magnetic tape system is employed as a signal source. In such systems, the term “display” means providing a capability for both audio and video signals. In systems that employ a continuous physical medium as a content storage and/or playback medium, it is difficult to synchronize multiple signal sources to provide a coordinated display of multiple images, some of which may be identical, or multiple different portions or “tiles” of a single image.
Additionally, such systems do not facilitate modification of the presentation “on the fly” and thus can make rehearsals, which frequently require modification of the score (e.g., rewinding for a revision of a given segment), cumbersome. In other words, if need to replay a portion of the presentation presents itself during the presentation or rehearsal, the medium must be physically rewound, a specific portion corresponding to the portion to be replayed must be located, and the display process re-initiated. Similarly, when it is determined that a portion of a pre-recorded display should be skipped, there is need to fast forward the medium, locate a desired portion and restart the display process. Such results in interruption of the presentation, which detracts from the audience appreciation of the content that is being presented.
Additionally, the types of machinery used in such systems, such as video tape recorders and film projectors, tend to be quite expensive. One approach to ensuring uninterrupted operation of an electronic system is to run a primary system in tandem with a backup system that is switched to the role of the primary system when problems develop in the primary system. However, when there is need to provide multiple images for a particular event, the costs associated with providing multiple backup systems become inconvenient. This is especially true when the event is a one-time event, such as an annual meeting, symposium or the like.
When multiple audio-visual displays are employed to try to provide a large audience with access to a particular presentation, such as a speaker addressing a large audience, there is need to maintain synchronization between the images and more particularly between the images and any related sound tracks. When the sound tracks are not synchronized with each other, or when the sound track is not synchronized with the image, the perceptual discordance of the presentation tends to undesirably detract from intelligibility and audience appreciation of the content being presented.
As an example, studies and experiments have yielded a generally-accepted standard of a range of a relative delay of a negative eight milliseconds and a positive twenty to thirty milliseconds of synchronization between sound and visual display to avoid viewer/listener perception of the relative delay and thus to avoid distraction from the content.
Further, large amounts of media having video and audio-visual content have been recorded since the inception of such systems. As such systems developed and realized increasing sophistication, a variety of standards were deployed in order that such recorded media could be distributed over wide geographic areas and used to provide relatively constant quality and intelligibility. For example, a number of such standards have been put forth by the Society of Motion Picture and Television Engineers and these are generally referred to as SMPTE standards. When a presentation relies on an ensemble of disparately-recorded video streams, it is necessary to be able to process data recorded using these various different standards, which, in turn, complicates synchronization of multiple displays.
Accordingly, there are needs for improved techniques, systems and apparatus for providing more robust synchronization of multiple video and/or audio-visual displays or data streams together with improved ability to arbitrarily shift from one point to another in such data streams in synchrony.